Spark ignition internal combustion engines are well known in the art. Such engines operate by exposing an air/fuel mixture to a spark. The resulting explosion creates force that the engine translates into mechanical work. The efficiency of the combustion process depends, at least in part, on the ratio of air to fuel. This parameter can be calculated and utilized in a closed loop system to control the combustion process through appropriate use of a strategically located oxygen sensor, all as well understood in the art.
So long as the oxygen sensor provides accurate data, a closed loop control system as described above can effectively and efficiently control fuel delivery to an internal combustion engine. Open loop control, of course, could also be effectuated by making assumptions regarding the missing parameter. Unfortunately, such assumptions are typically inaccurate, and continuous open loop control of a fuel delivery system yields far less efficiency than a closed loop system that utilizes input from an appropriately located oxygen sensor.
Oxygen sensors are typically formed of zirconium oxide material. These sensors typically provide an output signal that fluctuates between zero and one volt depending upon the oxygen concentration sensed. Unfortunately, these sensors are somewhat temperature dependent and their performance characteristics can also change over time. Further, continuous reliable receipt of oxygen sensor signals cannot always be assured for a variety of reasons. Therefore, oxygen sensors typically provide nonuseful data during the initial cranking phases of engine operation, and also may experience transient dropouts from time to time during normal operation.
One prior art response has been to continuously maintain closed loop control regardless of the validity of the incoming oxygen sensor data. When the oxygen sensor faults for long periods of time, however, this can have highly detrimental impact on engine efficiency and operation. Another prior art approach has been to switch to open loop control upon sensing that the oxygen sensor has faulted. Since such sensors are subject to frequent periods of nonuseful operation, this can result in long periods of open loop control that do not provide optimum operation of the engine in question.
There therefore exists a need for an oxygen sensor fault detection and response system that allows a fuel delivery system to detect and appropriately respond to a faulty oxygen sensor input, without unduly compromising or restricting ability of the system to accommodate the transient operating capabilities of oxygen sensors in general.